1. Field of the Invention
The invention relates to a brake control apparatus and brake control method that controls the braking force applied to the wheels of a vehicle.
2. Description of the Related Art
Japanese Patent Application Publication No. 2005-35471 (JP-A-2005-35471) describes a hydraulic pressure control apparatus that controls the braking force applied to the wheels of a vehicle. The hydraulic pressure control apparatus is provided with an actuator that includes a pair of electromagnetic control valves respectively used to increase and decrease the pressure of the hydraulic fluid supplied to a wheel cylinder provided at each wheel; and an electronic control unit that controls the actuator. In this hydraulic pressure control apparatus, the operation amount of a brake pedal is measured by, for example, a sensor, and translated into an electric signal that is transmitted to the electronic control unit. The electronic control unit controls the electromagnetic control valve that changes the pressure, thereby controlling the pressures of the hydraulic fluid supplied to the wheel cylinders for the four wheels of the vehicle independently from each other in an optimum manner. Accordingly, the vehicle runs highly stably and safely. Controlling the braking force based on electric signals translated from the operations executed by the driver is generally referred to as “brake by wire”.
Japanese Patent Application Publication No. 2006-15876 (JP-A-2006-15876) describes a brake control apparatus provided with a shut-off valve that shuts off communication between a master cylinder and the wheel cylinders; and electric power supply amount control means for changing the amount of electric power supplied to a coil of the shut-off valve in accordance with the magnitude of hydraulic pressure detected by hydraulic pressure detection means. With this brake control apparatus, the amount of heat released from the shut-off valve is reduced, which allows the use of a smaller coil.
In the apparatus described above, however, the flow of the hydraulic fluid delivered from the master cylinder in response to a brake pedal operation is interrupted instead of being permitted to reach the wheel cylinders during the control through brake-by-wire. Accordingly, if the wheel cylinder pressure abruptly drops due to, for example, occurrence of a malfunction, or the master cylinder pressure abruptly increases due to a sudden brake pedal operation, the response of the braking force to the braking operation may be affected due to a delay of control or a delay of detection inherent in a control system.